Various conditions can adversely affect the dental health of animal patients such as dogs and cats. If untreated, these conditions can develop into more serious illnesses, possibly leading to debilitating diseases and even death. For example, although the presence of quantities of bacteria in the mouth of a patient is normal, if the numbers of bacteria become too large they can lead to periodontitis, or periodontal disease. Periodontal disease frequently results in loss of teeth, and may also lead to serious bacterial infections and related illnesses if left untreated, as described below.
Periodontal disease in animals typically leads to recession of the gingiva (gums) in areas surrounding the diseased teeth. This recession of the gums may advance far enough so that a tooth becomes loose, at which point large quantities of bacteria may be released into the blood stream. Bacteria released by periodontitis in this manner may travel to any part of the body, including the heart, lungs, and kidneys, possibly leading to serious infections of those organs. Animals must therefore receive periodic dental care in order to prevent and/or treat periodontal disease, and to remain healthy.
In addition to periodontal disease, other dental conditions in animals may require examination and/or treatment by a veterinarian. These include, for example, chipped or broken teeth, abscesses, caries (cavities), and oral lesions of various types, among others. Accurate dental x-rays are crucial for the pre-treatment diagnosis of these conditions, and also often are used to confirm that treatment has been successful. For instance, dental x-rays may aid in the pre-treatment diagnosis of an abscessed tooth, and also may be used after a root canal procedure, to verify that the pulp cavity and root canal have been completely filled.
Dental x-rays are typically obtained by directing a collimated x-ray beam from an x-ray head towards an intraoral x-ray film, with one or more target teeth of the patient disposed between the x-ray head and the film. The least distortion of the resulting radiographic image occurs when the x-ray film and the target teeth are parallel to each other and orthogonal to the beam, with the film just behind the target teeth. However, for most animal patients, this parallel technique is only possible when obtaining x-rays of the lower rear teeth (caudal mandibular view). For all other views, the shape of the animal's palate and/or other factors prevent using the parallel technique, and the least distortion is obtained using the bisecting-angle technique.
In the bisecting-angle technique, an x-ray film plane is defined by the plane of the x-ray film, and a target plane is defined by an axis through a target tooth. A bisecting plane is defined by the angle that bisects the x-ray film plane and the target plane, and the x-ray beam is directed orthogonal to the bisecting plane. This technique leads to a radiographic image in which the image of the target tooth has approximately the same height as the tooth itself. More specifically, portions of the image corresponding to cross sections of the target tooth taken parallel to the target plane have the same sizes in the x-ray as the corresponding actual cross sections of the tooth.
Typically, a veterinarian or a veterinary technician estimates the target plane, the bisecting angle, and the corresponding bisecting plane by inspection during an x-ray procedure. Furthermore, aligning the x-ray beam orthogonal to the estimated bisecting plane also typically is done by inspection. In some cases, this procedure may lead to errors in determining the bisecting plane and/or aligning the x-ray beam orthogonal to the bisecting plane. This may result in foreshortened, elongated, and/or otherwise distorted radiographic images on the film.